1. Field of the Invention
The present invention relates generally to an antenna system for receiving a television broadcast wave, a radio broadcast wave and so on, and is directed more particularly to an antenna system whose direction and directivity characteristic can be varied.
2. Description of the Prior Art
In general, the arriving direction of a broadcast wave at an antenna system differs dependent upon the broadcast station whose signals are being received. There are two cases. One of them is the simplest case where the position of a transmission antenna is different from that of a broadcast station. The other case is one where electric waves from different stations are being broadcast from a single transmission antenna system, and the directions of the broadcast waves arriving at a receiving antenna system become different due to reflection and diffraction of the waves or frequencies thereof. Further, there may be situations where even if the same wave is broadcast, it may be separated by the reflection and diffraction into a plurality of waves and the separated waves arrive at the receiving antenna system from different directions.
In general, a portable antenna system is located in a room so that the above diffraction and reflection of the wave appear remarkably.
Therefore, it is required that the direction and directivity characteristic of the receiving antenna system be varied in accordance with the wave of a station to be received. For example, the portable antenna system is manually moved to vary its directivity characteristic or direction. In this case, since a user contacts or is near the antenna (antenna conductor), its directivity characteristic or arriving manner of waves becomes different. Therefore, there may be a concern that when the user is separated from the antenna system or device, even if the antenna device is positioned optimum to receive the wave, the receiving state becomes deteriorated.
To avoid the above defect, there has been proposed in the art that in order to remotely vary the direction of an antenna device, a motor be provided on the antenna device and that the motor be remotely controlled through a control line to thereby rotate the antenna, and hence to vary the direction of the antenna.
With the above antenna device, however, a noise is generated by the rotation of the motor and this noise affects the reception at the receiver. A mechanical noise generated by the rotation of the motor is also discomfortable to a user.